In the past few years, 17-keto steroids have become much more readily available as starting materials for corticoid synthesis because of the discovery of a number of microorganisms which will cleave the C.sub.17 side chain of various steroid substrates, see U.S. Pat. Nos. 4,035,236, 3,684,657 and 3,759,791.
U.S. Pat. No. 4,041,055 claims a process for producing 17.alpha.-hydroxyprogesterone and corticoids from 17-keto steroids. The first step is addition of a 2-carbon moiety by formation of ethisterone. This is followed (1) by reaction with phenylsulfenyl chloride to form an allene sulfoxide, (2) Michael addition to form a sulfoxide, (3) reaction with a thiophile and (4) reaction with a peracid to give the 17.alpha.,21-dihydroxy-20-keto corticoid side-chain.
U.S. Pat. No. 4,216,159 claims a process of transforming a 17-keto steroid to the corresponding 16-unsaturated-21-hydroxy-20-keto steroid by reaction with a lithiated chlorovinyl ether. The objective of that patent is to produce .DELTA..sup.16 -C.sub.21 steroids which can then be used to make C.sub.16 functionalized corticoids.
The process of the present invention does not involve lithiated chloro vinyl ethers and does not produce .DELTA..sup.16 -C.sub.21 steroids.
The process of the present invention is similar to the process of U.S. Pat. No. 4,041,055 in that it transforms a 17-keto steroid to the corresponding corticoid, but does so by a different synthetic pathway.
The base catalyzed isomerization of .beta., .gamma. to .alpha.,.beta.-unsaturated sulfoxides is well known, see J. Am. Chem. Soc. 86, 3840 (1964) and the addition of nucleophiles to .beta.-halo-.alpha.,.beta.-unsaturated sulfoxides has been previously observed in simple systems, see J. Org. Chem. 35, 2831 (1970).